Operations with oriented angles

Question

If I have the figure below, how can I get the angle $a_2$ (the angle is >0 in counterclockwise direction)?

$$a_2 = \frac{\pi}{2} + a_1$$

or

$$a_2 = \frac{\pi}{2} - a_1$$ ?

Thank you for your help.

Answer 1

We have $$|-\alpha_1| + \alpha_2 = \frac{\pi}2$$

since $$\alpha_2 = \frac{\pi}2 - |-\alpha_1|= \frac{\pi}2 - |\alpha_1|= \frac{\pi}2 - \alpha_1$$